This invention relates to glass manufacturing and, in particular, to the problem of separating panes of glass from a moving ribbon of glass without excessive generation of glass chips through edge contact and resulting damage.
More generally, the invention relates to separating panes of any brittle material from a moving ribbon of the material. For ease of presentation, however, the following discussion is in terms of glass manufacturing, it being understood that the invention as defined in the appended claims is not so limited except for those claims which specify that the brittle material is glass.
Specialized glasses such as those used as substrates in the manufacture of liquid crystal displays and similar devices have demanding standards regarding surface defects. One source of such defects is glass chips generated during the separation of panes of glass from a moving ribbon of glass.
In the past, such separation has been performed manually using the following steps. First, a separation line (score line) was formed in the ribbon of glass using an automated moving scribe/moving anvil assembly. Then, the operator attached a vacuum cup array to the glass below the score line and applied a bending moment to the glass to cause it to break at the score line and thus form the desired glass pane. This breaking produced a newly-formed leading edge on the moving ribbon and a newly-formed trailing edge on the glass pane.
To avoid damage to these newly-formed edges, the operator would endeavor to immediately move the pane away from the oncoming leading edge of the ribbon. As will be evident, this was not easy to do because, among other things, it was difficult to apply the same bending moment to the pane each time it was to be separated form the moving ribbon. Different bending moments resulted in different orientations for the pane at the time of separation, making it even more difficult to avoid edge contact. Different bending moments also affect the break signature or quality of the break independent of edge contact. Moreover, even with identical bending moments, individual panes of glass can separate at different angles making the avoidance of edge contact even more difficult to achieve.
As a result, only highly skilled and trained operators could perform the pane separation procedure, and even with such operators, edge contact and break signature variation occurred leading to rejected panes.
In view of the foregoing, it is an object of the present invention to provide methods and apparatus for overcoming the problem of edge contact during the separation of a pane of a brittle material from a moving ribbon of the material. It is also an object of the invention to provide methods and apparatus for applying a repeatable, uniform bending moment to a pane of a brittle material to separate the pane from a moving ribbon of the material.
To achieve these and other objects, the invention in accordance with one of its aspects provides apparatus for separating a pane (11) of a brittle material from a moving sheet (13) of the material along a separation line (47), said pane and said sheet having a width W, said pane when separated having a length L, said movement of the sheet being described by a vector {overscore (V)}sheet, said apparatus comprising:
(a) a pane engaging assembly (15) adapted to releasably engage the moving sheet within an area defined by the length L and width W of the to-be-separated pane;
(b) a transporter (29) adapted to bring the pane engaging assembly into engagement with the moving sheet and to rotate that assembly about an axis which substantially coincides with the separation line, said rotation causing the pane to separate from the sheet; and
(c) a connector assembly (31) for connecting the pane engaging assembly and the transporter so that the pane engaging assembly moves relative to the transporter upon separation of the pane from the moving sheet so that the pane and the sheet do not contact each other once separation occurs.
In accordance with other aspects, the invention provides a method for separating a pane (11) of a brittle material from a moving sheet (13) of the material along a separation line (47), said pane and said sheet having a width W, said pane when separated having a length L, said movement of the sheet being described by a vector {overscore (V)}sheet, said method comprising:
(a) releasably engaging the moving sheet (13) within an area defined by the length L and width W of the to-be-separated pane;
(b) rotating the to-be-separated pane about an axis which substantially coincides with the separation line, said rotation causing the pane to separate from the sheet; and
(c) moving the separated pane relative to the moving sheet either passively using gravity as the motive force (i.e., the sole motive force) or actively using at least one of a hydraulic force, a mechanical spring force, a pneumatic force, and a vacuum, either alone or in combination with gravity, as the motive force, so that the pane and the sheet do not contact each other once separation occurs.
FIG. 1 illustrates the operating principles of the invention. As shown therein, pane engaging assembly 15 has been brought into engagement with a moving ribbon 13 of a brittle material. As indicated by arrows 51, both the pane engaging assembly and the ribbon of brittle material are moving with substantially the same speed in substantially the same direction at the instant shown, i.e., they each have substantially the same vector velocity. As also shown in the figure, a score line 47 has been formed in the brittle material and a stop 49 is in position so that a bending moment can be applied about the score line. The score or separation line is substantially perpendicular to the vector {overscore (V)}sheet and defines the length L of the to-be-separated pane. It can be formed by a scoring assembly 21 of the type discussed below or other scoring assemblies known in the art.
Arrows 53 and 55 represent the forces that, in accordance with the invention, are brought to bear so that (1) the pane becomes separated from the ribbon and (2) the pane immediately moves away from the ribbon once separation has been achieved.
In particular, arrow 53 represents a bending moment that is applied to the pane through the pane engaging assembly and causes the pane to separate from the ribbon at the score line. As can be seen in FIG. 1, this bending moment is applied by rotating the pane engaging assembly about score line 47. In this way, a pure bending moment is applied to the score line which causes it to open up and drive through the sheet. As discussed in detail below, transporter 29 acting through connector 31 produces this rotation (see FIGS. 4-5).
Arrow 55 represents a force which moves the separated pane away from the still advancing ribbon. The force can be an active force, a passive force, or a combination of an active and passive force. FIG. 1 shows the system in a horizontal orientation in which case the force needs to be an active force, e.g., a hydraulic force, a mechanical spring force, a pneumatic force, a vacuum, or the like. For a vertical orientation, the pane can move passively away from the ribbon under the force of gravity.
Force 55 acts on the separated pane through the cooperation of pane engaging assembly 15, transporter 29, and connector assembly 31 (see, for example, FIGS. 5 and 12). For active systems, the connector assembly allows the active force to produce relative motion between the pane engaging assembly/separated pane combination and the transporter. Such an active force can originate from, for example, a force generator, e.g., a pneumatic cylinder, mounted on the connector assembly, the transporter, and/or some other part of the apparatus or its housing. In the case of a passive system which uses gravity as a motive force, the connector assembly allows the pane engaging assembly/separated pane combination to undergo a controlled xe2x80x9cfallxe2x80x9d relative to the transporter so that the pane falls away from the moving ribbon.
It should be noted that through the application of bending moment 53, some rotation of the pane about score line 47 will take place and thus force 55 will no longer be parallel to velocity vector 51 when it performs its function of moving the pane away from the leading edge of the moving ribbon. For example, for a typical liquid crystal display glass having a thickness of about 0.7 millimeters with a score line which penetrates 10% or less of the thickness of the sheet, separation will normally take place at an angle greater than zero and less than about 10xc2x0. All that is required, however, is that force 55 has a component in the direction of vector 51 that is sufficient to move the pane away from the leading edge of the ribbon once separation has occurred, not that the force is parallel to vector 51.
Additional features and advantages of the invention are set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein.